SCH3112I-NE SMSC [SMSC Corporation], SCH3112I-NE Datasheet - Page 237

• Manufacturer Part Number: SCH3112I-NE
• Description: LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
• Manufacturer: SMSC [SMSC Corporation]

LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
Datasheet
SMSC SCH311X
23.14.2.8
FREQUENCY
PWM
(HZ)
87.7
58.6
35.2
29.3
21.9
14.6
44
11
Note: The Slow Interrupt Enable feature (SLOW) is configured in the TACHx Options registers at
■
Notes:
■
■
Examples of Minimum RPMs Supported
The following tables show minimum RPMs that can be supported with the different parameters. The
first table uses 3 edges and the second table uses 2 edges.
Note 23.1 100% duty cycle is 255/256
Note 23.2 RPM=60/T
The programmed number of edges occurs:
-Mode 1: If the programmed number of edges occurs before the counter reaches FFFFh latch the
tachometer count
-Mode 2: If the programmed number of edges occurs during the PWM ‘ON’ time: latch the
tachometer count (see Note below).
Whenever the programmed number of edges is detected, the edge detection ends and the state
machine is reset. The tachometer reading register is updated with the tachometer count value at
this time. See
In the case where the programmed number of edges occurs during the “on”, the tachometer value
is latched when the last required edge is detected.
(MSEC)
offsets 90h to 93h.
11.42
17.12
22.73
25%
2.85
4.27
5.68
8.53
PULSE WIDTH AT DUTY CYCLE
7.1
(PWM ”ON” Time – Guard Time). Minimum RPM values shown use minimum guard time
(88.88usec).
Table 23.5 Minimum RPM Detectable Using 3 Edges
(PWM ”ON” TIME)
Detection of a Stalled Fan on page 222
(MSEC)
11.36
17.06
22.83
34.25
45.45
Revolution
50%
8.53
14.2
5.7
, T
TachPulse
(NOTE 23.1)
DATASHEET
(MSEC)
100%
11.36
22.64
45.48
68.23
90.55
28.3
17
34
221
= T
Revolution
MINIMUM RPM AT DUTY CYCLE (NOTE 23.2)
10865
7175
5366
4279
3554
2648
1761
1325
/2. Using 3 edges for detection, T
25%
for the exception to this behavior.
(30/T
5347
3554
2662
2126
1768
1319
50%
878
661
TachPulse
)
Rev 0.2 (09-28-04)
100%
2662
1774
1330
1063
885
661
440
332
TachPulse
=